The effect of magnetic nanofilm morphology on spintronic terahertz emission performance

Femtosecond laser-driven spintronic terahertz (THz) emitters based on magnetic nanofilms are poised to be the next-generation mainstream THz radiation devices due to their low cost, high performance, ultra-broadband, and easy integration. The radiation performance of spintronic THz emitters is related to the material characteristics, heterostructure interfaces, pump laser, and magnetic field intensity. Additionally, the THz emission performance is greatly reliant on the material surface morphology. Here, we employed ultrafast THz scattering-type scanning near-field optical microscopy with nanoscale spatial resolution to obtain the static THz scattering nano-imaging of ferromagnetic/antiferromagnetic heterostructures (W/Co20Fe60B20/IrMn3). We established the relationship between surface morphology and THz scattering intensity. Utilizing laser-induced THz emission technology, we achieve injection and detection of nanoscale ultrafast spin current without the external magnetic field. The strong consistency of the THz emission nanoscopy with the atomic force microscopy topography demonstrates that the sample surface morphology is critical to the THz radiation performance. This study serves as a valuable reference for the further optimization of spintronic THz emitters and promotes the development of high-performance, strong-field spintronic THz sources.